linux-kernel - [RFC PATCH 7/9] drivers/dax: add protected memory bit to dev

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Message-ID: <20251107224956.477056-8-gourry@gourry.net>
Date: Fri,  7 Nov 2025 17:49:52 -0500
From: Gregory Price <gourry@...rry.net>
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Subject: [RFC PATCH 7/9] drivers/dax: add protected memory bit to dev_dax

This bit is used by dax/kmem to determine whether to set the
MHP_PROTECTED_MEMORY flags, which will make whether hotplug memory
should be restricted to a protected memory NUMA node.

Signed-off-by: Gregory Price <gourry@...rry.net>
---
 drivers/dax/bus.c         | 39 +++++++++++++++++++++++++++++++++++++++
 drivers/dax/bus.h         |  1 +
 drivers/dax/dax-private.h |  1 +
 drivers/dax/kmem.c        |  2 ++
 4 files changed, 43 insertions(+)

diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
index fde29e0ad68b..4321e80276f0 100644
--- a/drivers/dax/bus.c
+++ b/drivers/dax/bus.c
@@ -1361,6 +1361,43 @@ static ssize_t memmap_on_memory_store(struct device *dev,
 }
 static DEVICE_ATTR_RW(memmap_on_memory);
 
+static ssize_t protected_memory_show(struct device *dev,
+				     struct device_attribute *attr, char *buf)
+{
+	struct dev_dax *dev_dax = to_dev_dax(dev);
+
+	return sysfs_emit(buf, "%d\n", dev_dax->protected_memory);
+}
+
+static ssize_t protected_memory_store(struct device *dev,
+				      struct device_attribute *attr,
+				      const char *buf, size_t len)
+{
+	struct dev_dax *dev_dax = to_dev_dax(dev);
+	bool val;
+	int rc;
+
+	rc = kstrtobool(buf, &val);
+	if (rc)
+		return rc;
+
+	rc = down_write_killable(&dax_dev_rwsem);
+	if (rc)
+		return rc;
+
+	if (dev_dax->protected_memory != val && dev->driver &&
+	    to_dax_drv(dev->driver)->type == DAXDRV_KMEM_TYPE) {
+		up_write(&dax_dev_rwsem);
+		return -EBUSY;
+	}
+
+	dev_dax->protected_memory = val;
+	up_write(&dax_dev_rwsem);
+
+	return len;
+}
+static DEVICE_ATTR_RW(protected_memory);
+
 static umode_t dev_dax_visible(struct kobject *kobj, struct attribute *a, int n)
 {
 	struct device *dev = container_of(kobj, struct device, kobj);
@@ -1388,6 +1425,7 @@ static struct attribute *dev_dax_attributes[] = {
 	&dev_attr_resource.attr,
 	&dev_attr_numa_node.attr,
 	&dev_attr_memmap_on_memory.attr,
+	&dev_attr_protected_memory.attr,
 	NULL,
 };
 
@@ -1494,6 +1532,7 @@ static struct dev_dax *__devm_create_dev_dax(struct dev_dax_data *data)
 	ida_init(&dev_dax->ida);
 
 	dev_dax->memmap_on_memory = data->memmap_on_memory;
+	dev_dax->protected_memory = data->protected_memory;
 
 	inode = dax_inode(dax_dev);
 	dev->devt = inode->i_rdev;
diff --git a/drivers/dax/bus.h b/drivers/dax/bus.h
index cbbf64443098..0a885bf9839f 100644
--- a/drivers/dax/bus.h
+++ b/drivers/dax/bus.h
@@ -24,6 +24,7 @@ struct dev_dax_data {
 	resource_size_t size;
 	int id;
 	bool memmap_on_memory;
+	bool protected_memory;
 };
 
 struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data);
diff --git a/drivers/dax/dax-private.h b/drivers/dax/dax-private.h
index 0867115aeef2..605b7ed87ffe 100644
--- a/drivers/dax/dax-private.h
+++ b/drivers/dax/dax-private.h
@@ -89,6 +89,7 @@ struct dev_dax {
 	struct device dev;
 	struct dev_pagemap *pgmap;
 	bool memmap_on_memory;
+	bool protected_memory;
 	int nr_range;
 	struct dev_dax_range *ranges;
 };
diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
index c036e4d0b610..140c6cb0ac88 100644
--- a/drivers/dax/kmem.c
+++ b/drivers/dax/kmem.c
@@ -169,6 +169,8 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
 		mhp_flags = MHP_NID_IS_MGID;
 		if (dev_dax->memmap_on_memory)
 			mhp_flags |= MHP_MEMMAP_ON_MEMORY;
+		if (dev_dax->protected_memory)
+			mhp_flags |= MHP_PROTECTED_MEMORY;
 
 		/*
 		 * Ensure that future kexec'd kernels will not treat
-- 
2.51.1